The invention relates to a polarization-sensitive beam splitter having a polarization-separating layer interposed between two transparent elements, said polarization-separating layer comprising a birefringent material.
The invention also relates to a method of manufacturing a polarization-sensitive beam splitter, in which a polarization-separating layer is interposed between two transparent elements.
According to the state of the art a polarization-sensitive beam splitter can be manufactured in the form of a Wollaston prism as described in McGraw-Hill Encyclopedia of Science and Technology, vol 10, page 499 (1960). To avoid the use of birefringent prisms, a polarization-separating layer which is interposed between two transparent elements can be used in known manner. There elements may be composed of ordinary glass or a synthetic resin having the same single refractive index, see United States Patent Specification U.S. Pat. No. 4,702,557. In this specification, the polarization-separating birefringent layer consists of a liquid-crystalline layer having a thickness of 5 to 10 .mu.m. One of the refractive indices of said layer must be equal to the refractive index of the elements and the other refractive index must be smaller than the refractive index of the elements.
According to the state of the art, a thin liquid-crystalline layer is applied between two substrates (the transparent elements) by means of capillary forces. Means for sealing the thin layer from the environment must be provided. Further, it is necessary to position and secure the two substrates at a fixed distance from each other. A further disadvantage of the known devices is the difficulty of providing suitable liquid-crystalline materials having the above-described refractive indices. Moreover, the temperature resistance of liquid-crystalline layers is generally small.